Problem: Nauuo is a girl who loves playing chess.

One day she invented a game by herself which needs n chess pieces to play on a m× m chessboard. The rows and columns are numbered from 1 to m. We denote a cell on the intersection of the r-th row and c-th column as (r,c).

The game's goal is to place n chess pieces numbered from 1 to n on the chessboard, the i-th piece lies on (r_i,\,c_i), while the following rule is satisfied: for all pairs of pieces i and j, |r_i-r_j|+|c_i-c_j|≥|i-j|. Here |x| means the absolute value of x.

However, Nauuo discovered that sometimes she couldn't find a solution because the chessboard was too small.

She wants to find the smallest chessboard on which she can put n pieces according to the rules.

She also wonders how to place the pieces on such a chessboard. Can you help her?

Input

The only line contains a single integer n (1≤ n≤ 1000) — the number of chess pieces for the game.

Output

The first line contains a single integer — the minimum value of m, where m is the length of sides of the suitable chessboard.

The i-th of the next n lines contains two integers r_i and c_i (1≤ r_i,c_i≤ m) — the coordinates of the i-th chess piece.

If there are multiple answers, print any.

Examples

Input


2


Output


2
1 1
1 2

Input


4


Output


3
1 1
1 3
3 1
3 3

Note

In the first example, you can't place the two pieces on a 1×1 chessboard without breaking the rule. But you can place two pieces on a 2×2 chessboard like this:

<image>

In the second example, you can't place four pieces on a 2×2 chessboard without breaking the rule. For example, if you place the pieces like this:

<image>

then |r_1-r_3|+|c_1-c_3|=|1-2|+|1-1|=1, |1-3|=2, 1<2; and |r_1-r_4|+|c_1-c_4|=|1-2|+|1-2|=2, |1-4|=3, 2<3. It doesn't satisfy the rule.

However, on a 3×3 chessboard, you can place four pieces like this:

<image>

Solution (in JAVA):

Solution:
import java.io.*;
import java.util.*;

public class tmp
{
    
    static ArrayList<Integer> problem=new ArrayList<>();
    static PrintWriter out=new PrintWriter((System.out));
    static int maxInt=Integer.MAX_VALUE;
    static long maxLong=100000000000L;
    static long[][] dp;
    //static int n,p,k,x,y;
    static Reader sc=new Reader();
    public static void main(String args[])throws IOException
    {
        
        // int t=sc.nextInt();
        
        // while(t-- >0){
            solve();
        // }
        
    	out.close(); 
    }

    public static void solve(){
        int n=sc.nextInt();
        out.println(n/2+1);
        int i=1,j=1,flag=0;
        while(n-- >0){
            if(flag==0){
                out.println(i+" "+j);
                j++;
            }else{
                out.println(i+" "+j);
                i++;
            }
            flag=1-flag;
        }
        
    }
    static boolean isSorted(int[] arr){
        for(int i=0;i<arr.length-1;i++){
            if(arr[i]>arr[i+1]){
                return false;
            }
        }
        return true;
    }
    public static long pow(long a,long b){
        if(b==0){
            return 1;
        }
        if(b%2==0){
            return pow(a*a,b/2);
        }else{
            return a*pow(a*a,b/2);
        }
    }
    static class Reader {
		BufferedReader br=new BufferedReader(new InputStreamReader(System.in));
		StringTokenizer st=new StringTokenizer("");
		String next() {
			while (!st.hasMoreTokens())
				try { 
                   st=new StringTokenizer(br.readLine());				               
                } catch (IOException e) {}
			return st.nextToken();
		}
		
		int nextInt() {
			return Integer.parseInt(next());
		}
		long nextLong() {
			return Long.parseLong(next());
		}
	}
}